Recent advances and challenges in the design of Li-air batteries oriented solid-state electrolytes

Solid-state Li-air batteries with ultrahigh energy density and safety are promising for long-range electric vehicles and special electronics. However, the challenging issues of developing Li-air battery-oriented solid-state electrolytes (SSEs) with high ionic conductivity, interfacial compatibility, and stability to boost reversibility, increase stable triple-phase boundaries, and protect the Li anode in an open system substantially impede their applications. Herein, we systematically summarize the recent progress achieved in terms of SSEs for Li-air batteries, and describe in detail the basic characteristics of SSE|air cathode interfaces and SSE|Li anode interfaces. First, the major characteristics of SSEs in Li-air batteries in terms of ionic/electronic conductivity, chemical/electrochemical/thermal stability, mechanical strength, and interfacial compatibility are briefly introduced according to three types of SSEs: inorganic, organic, and hybrid SSEs. Second, key strategies of integrating catalytic sites, porous structures, and electronic conductors with SSEs to enhance triple-phase boundaries at the SSE|air cathode for improving Coulombic efficiency are described in detail. Moreover, the protection of Li metal from H2O, CO2, O-2, and redox mediators at the SSE|Li anode to ensure safety is elaborately overviewed. Finally, future opportunities and perspectives on three important topics of three-dimensional structural integration, external field assistance, and operando characterizations are proposed for advanced solid-state Li-air batteries.